First off, Enigma and other Allied code-breaking successes against the Germans only became public knowledge after 1974 when the British government confirmed the accuracy of F. W. Winterbotham's book The Ultra Secret shortly after its publication. There had been some claims to breaking Enigma prior to Winterbotham's book, most notably the 1967 Polish book Bitwa o tajemnice (Battle for Secrets) by Wladyslaw Kozaczuk which revealed that Polish cryptographers had broken Enigma. Other books treated Ultra more gingerly. For example, 1972's The Double-Cross System: The Incredible True Story of How Nazi Spies Were Turned into Double Agents by J. C Masterman never mentioned cryptoanalysis but revealed the extent to which German agents had been compromised by the British. The first edition of David Kahn's 1967 opus The Codebreakers mentioned that the Soviets had broken Enigma and outlined some of the individual successes American code-breakers had during the war. Although neither author referenced codebreaking efforts against Germany directly, it was notable by its conspicuous absence.

Prior to 1974, both German historians and veterans were quite dismissive of any notion that their cryptographic system had been broken and their measures were for naught. Two German reviews of Kozaczuk dismissed his claims and other veterans described the idea that the Poles could have cracked Enigma as "wishful thinking." Heinz Bonatz, the former head of the Kriegsmarine's B-Dienst wrote in his 1970 history of German naval intelligence Die deutsche Marine Funkaufklärung asserted that Enigma was never broken and Allied silence on this success confirmed that German security measures were sufficient. Bonatz instead blamed Allied successes on a myriad of other factors ranging from Humint, superior radio-direction finding equipment, to sloppy Italian code security. In short, the mainstream German opinion prior to 1974 ascribed Allied successes to everything except Enigma. After the UK government's confirmation of The Ultra Secret there were still some veterans in denial, but most German commentators were in shock about the scale to which their security system had been compromised.